1. Field of the Invention
The present invention generally relates to a spine formation device to form a spine of a bundle of folded sheets, a bookbinding system including the spine formation device and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine capable of at least two of these functions, and a method of processing a bundle of folded sheets.
2. Description of the Background Art
At present, saddle-stitching or saddle-stapling, that is, stitching or stapling a bundle of sheets along its centerline, is widely used as a simple bookbinding method. Typically, the spine of the bundle of sheets (hereinafter “a booklet”) produced through saddle-stitching bookbinding tends to bulge as a result of being folded along its centerline. It is preferable to reduce such bulging of the spine of the booklet, that is, to flatten the spine of the booklet, to improve its appearance and to facilitate stacking, storage, and transport of the booklets.
More specifically, when a bundle of sheets is saddle-stitched or saddle-stapled and then folded in two, the folded portion around its spine tends to bulge, degrading the overall appearance of the booklet. In addition, because the bulging spine makes the booklet thicker on the spine side and thinner on the opposite side, when the booklets are piled together with the bulging spines on the same side, the piled booklets tilt more as the number of the booklets increases. Consequently, the booklets might fall over when piled together.
By contrast, when the spine of the booklet is flattened, bulging of the booklet can be reduced, and accordingly multiple booklets can be piled together stably. This flattening is important for ease of storage and transport because it is difficult to stack booklets together if their spines bulge, making it difficult to store or carry them. With this reformation, relatively large number of booklets can be piled together. It is to be noted that the term “spine” used herein means not only the stitched side of the booklet but also portions of the front cover and the back cover continuous with the spine.
In view of the foregoing, for example, the following approaches have been proposed to flatten the spine of the booklet.
For example, in JP-2001-260564-A, the spine of the booklet is flattened using a pressing member configured to clamp simultaneously, from a front cover side and a back cover side of the booklet, an end portion of the booklet adjacent to the spine, and a spine-forming roller configured to roll along the spine longitudinally. The spine-forming roller rolls at least once over the entire length of the spine of the booklet fixed in place by the pressing member while applying to the spine a pressure sufficient to flatten the spine.
Although this approach can flatten the spine of the booklet to a certain extent, it is possible that the sheets might wrinkle and be torn around the spine or folded portion because the spine-forming roller applies localized pressure to the spine continuously. Further, it takes longer to flatten the spine because the spine-forming roller must move over the entire length of the spine of the booklet.
In view of the foregoing, for example, to shape the spine in a reduced time without damaging it, the bulging of the booklet may be squeezed gradually. More specifically, a conveyance unit transports a bundle of folded sheets to a position where the folded leading-edge portion of the bundle is pressed against a contact member and the folded leading-edge portion bulges. Then, the bundle is squeezed in the direction of thickness of the bundle gradually from the upstream side in the direction in which the bundle is transported, thereby localizing the bulging of the booklet to the downstream side. Then, the bundle of sheets is further squeezed with its folded leading-edge pressed against the contact member.
Moreover, at present, efficiency is preferred in flattening the spine of the booklet to reduce the energy required for spine formation. The first approach described above using the spine-forming roller may not be very efficient or energy-saving because the only thing that can be adjusted is the number of times the spine-forming roller rolls on the spine of the booklet.
In view of the foregoing, the inventors of the present invention recognize that there is a need to enhance efficiency in processing the booklet to save energy and time required for the processing as well as to reduce damage to the booklet, which known approaches fail to do.